Key Science Goals for the Next-Generation Event Horizon Telescope

Abstract

The Event Horizon Telescope (EHT) has led to the first images of a supermassive black hole, revealing the central compact objects in the elliptical galaxy M87 and the Milky Way. Proposed upgrades to this array through the next-generation EHT (ngEHT) program would sharply improve the angular resolution, dynamic range, and temporal coverage of the existing EHT observations. These improvements will uniquely enable a wealth of transformative new discoveries related to black hole science, extending from event-horizon-scale studies of strong gravity to studies of explosive transients to the cosmological growth and influence of supermassive black holes. Here, we present the key science goals for the ngEHT and their associated instrument requirements, both of which have been formulated through a multi-year international effort involving hundreds of scientists worldwide.

32 pages, 11 figures, accepted for publication in a special issue of Galaxies on the ngEHT (https://www.mdpi.com/journal/galaxies/special_issues/ngEHT_blackholes)

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• Conservation of distortion of gravitationally lensed images
• First Very Long Baseline Interferometry Detections at 870μm
• Constraining spherically symmetric metrics by the gap between photon rings
• The conceptual design of the 50-meter Atacama Large Aperture Submillimeter Telescope (AtLAST)
• A Lensing-Band Approach to Spacetime Constraints
• Near-Horizon Polarization as a Diagnostic of Black Hole Spacetime
• Survey of Radiative, Two-Temperature Magnetically Arrested Simulations of the Black Hole M87* I: Turbulent Electron Heating
• Probing the Merger Rates of Supermassive Black Holes and Galaxies with Gravitational Waves
• Hot-spots around Sagittarius A*: Joint fits to astrometry and polarimetry
• Dynamic and polarimetric VLBI imaging with a multiscalar approach
• Orbital configurations of spaceborne interferometers for studying photon rings of supermassive black holes
• The future ability to test theories of gravity with black-hole shadows
• Polarimetric Geometric Modeling for mm-VLBI Observations of Black Holes
• Measuring Black Hole Light Echoes with Very Long Baseline Interferometry
• Multi-Frequency Models of Black Hole Photon Rings from Low-Luminosity Accretion Disks
• Illuminating Black Hole Shadow with Dark Matter Annihilation
• Inferring Black Hole Spin from Interferometric Measurements of the First Photon Ring: A Geometric Approach
• Spacetime Measurements with the Photon Ring
• Forward Ray Tracing and Hot Spots in Kerr Spacetime
• Gravity versus astrophysics in black hole images and photon rings: Equatorial emissions and spherically symmetric space-times
• Probing neutrino production in blazars by millimeter VLBI
• Imaging the event horizon of M87* from space on different timescales
• Imaging fermionic dark matter cores at the center of galaxies
• Breaking black-hole uniqueness at supermassive scales
• WISE2MBH: A scaling-based algorithm for probing supermassive black hole masses through WISE catalogues
• Shadows of naked singularity in Brans-Dicke gravity
• Deep learning inference with the Event Horizon Telescope II. The Zingularity framework for Bayesian artificial neural networks
• Self-Gravitating Matter in Stationary and Axisymmetric Black Hole Spacetimes
• Photon ring autocorrelations from gravitational fluctuations around a black hole
• PyGRO: a Python Integrator for General Relativistic Orbits
• Overlapping of photon rings in black hole imaging
• Origin of the ring ellipticity in the black hole images of M87*
• Tracking X-ray Variability in Next Generation EHT LLAGN Targets
• The cylindrical jet base of M87 within 100$\mu \mathrm{as}$ of the central engine
• Jet formation studies in AGN: a search for new targets
• Effect of Earth's Oblateness on Black Hole Imaging Through Earth-Space and Space-Space VLBI
• $\text{Jipole}$: A Differentiable $\text{ipole}$-based Code for Radiative Transfer in Curved Spacetimes
• Gravitational Lensing in the Kerr Spacetime: An Analytic Approach for Light and High-Frequency Gravitational Waves
• Limiting the Yukawa Gravity through the Black Hole Shadows of Sgr A* and M87*
• Kilogauss magnetic field and jet dynamics in the quasar NRAO 530
• Revisiting Einstein's analogy: black holes as gradient-index lenses
• Magnification of Classical Multimessenger Signals in Stationary and Axisymmetric Spacetimes with Separable Equations of Motion
• Exploring black holes with multiple photon spheres by interferometric signatures
• Extreme magnetic fields around black holes
• Toward Optimisation of a Sub-Terahertz Spaceborne VLBI Mission
• Constraints on High-Frequency Gravitational Waves from Graviton-Photon Conversion in the M87 Galaxy
• $\text{GPUmonty}$: A GPU-accelerated relativistic Monte Carlo radiative transfer code
• Fabry-Pérot open resonant cavities for measuring the dielectric parameters of mm-wave optical materials
• Impacts of radiative cooling on the images of a black hole shadow and extended jets in two-temperature GRMHD simulations
• Beyond Sgr A* and M87*: Sub-Microarcsecond Black Hole Shadow Detection via Lunar-based Extremely Long Baseline Interferometry
• Sensitivities of Black Hole Images from GRMHD Simulations
• Extreme-Lensing Signatures Revealed by Correlations of Simulated Black-Hole Movies
• Spatially resolved spectral properties of M87* on event horizon scales